Abstract: The centrifugal rotor contains a distributor forming a conical wall having openings through which the central inlet chamber is connected to the separating space, the inlet chamber also being connected through a presedimentation space to a peripheral sludge space by way of an annular slot located radially outward from said openings. An annular flexible valve for the slot has one side directed toward the presedimentation space and an opposite side directed toward the peripheral sludge space, the valve being operable to close said slot when subjected to substantially equal liquid pressures on said sides thereof and to open the slot upon creation of a substantial pressure difference on said sides in response to opening of outlets from the peripheral sludge space.